Duplicate anagrams produced when the same vector occurs twice in sum

[matthewearl]

For example, for an input of "ABAB" and a word list of ["AB","BA"], the vector set {{A:1,B:1},{A:1,B:1}} is correctly generated by _find_anagram_vecs().

_expand_anagram_vecs() then maps this to four anagrams:

1. AB AB
2. AB BA
3. BA AB
4. BA BA

2 and 3 are equivalent. _expand_anagram_vecs() should be fixed to stop generating such duplicates.